Uveitis is swelling and inflammation of the uvea, the middle layer of the eye. The uvea consists collectively of the iris, the choroid, and the ciliary body. Uveitis can exist in the front of the eye (anterior uveitis or iritis), the middle region of the eye (intermediate uveitis), the back of the eye (posterior uveitis), or throughout the eye (panuveitis or diffuse uveitis). The most common form of uveitis is anterior uveitis, which involves inflammation in the front part of the eye, usually the iris. Anterior uveitis can be divided into acute and chronic types based on the duration of the inflammation. A further classification is granulomatous and non-granulomatous. Granulomatous uveitis presents with large, greasy precipitates on the corneal endothelium with large clumps of inflammatory cells present in the anterior chamber because of exuberant macrophage activity. Nongranulomatous uveitis presents with fine cornea endothelial precipitates and anterior chamber activity (clumps). Uveitis can be graded based on the number of cells present in the aqueous according to the Standardization of Uveitis Nomenclature (SUN). Slit-lamp examination is the standard method for assessment of the inflammatory reaction in case of uveitis. However clinical assessment is subjective and often difficult in eyes with corneal opacification.
Optical Coherence Tomography is a non-invasive, in-vivo imaging technique based on the back-scatter or reflectivity of light in a medium. In ophthalmic examinations, the beam of light produced by the OCT device scans the eye through the pupil and the image formation process records the back-scattering profile of the light at each location. The amount of scatter is indicative of the reflectivity of the tissue encountered, and a grayscale cross-sectional image is formed as the light beam sweeps across the field of view (FOV). OCT imaging has dramatically advanced ophthalmic diagnostic capabilities and led also to better understanding of ocular anatomy. It is an established basis of routine ophthalmic practice. Several implementations of OCT have been developed including time domain (TD-OCT) and frequency domain (FD-OCT) (spectral domain (SD-OCT) and swept-source (SS-OCT)).
The clumps of inflammatory cells present in the anterior chamber of patients with uveitis appear as bright or hyperreflective spots in OCT images. US 2009/0244485 describes a method for determining or assessing risk of uveitis based on the intensity levels of the image signal as compared to a database of normal and abnormal values. Agarwal et al compared manual and automated counting of the hyperreflective spots in OCT images of the hyperreflective spots in anterior chamber OCT (Agarwal et al “High Speed Optical Coherence Tomography for Imaging Anterior Chamber Inflammatory Reaction in Uveitis: Clinical Correlation and Grading” Am J Ophthalmology 147(3): 413-416 2009). The images were post-processed using Matlab.
The methods described above are based on a numerical count of the number of cell clumps. The present invention introduces the concept of using OCT for providing an automated measurement of the shape and volume of these clumps. A further inventive aspect is the classification of the clumps into different types such as pigment clumps and cell clumps based on the reflectivity, size, shape and other parameters. Differentiating cells and cell clumps from pigment clumps would allow the level of cells present (an indication of disease status) to be estimated independent of surgical events that might release pigment from the iris into the anterior chamber.